Most WHATWG standards are hosted on GitHub.
To run the standard's Makefile (i.e. to run "make" in your terminal) you need to have whatwg/xref in the same parent directory as the repository of your standard (e.g. whatwg/dom). In addition you need to have installed Anolis (ms2ger/anolis).
Although some repositories are marked as "forked from" by GitHub, they are now the "authoritative" copies (indeed, also per their original owner).